1. Field of the Invention
The present invention relates to a long-lived cleaning vessel for ultrasonic cleaning, which is easily manufactured and is also easy to handle due to a simple structure thereof and which has excellent durability, mechanical strength, and resistance to corrosion. Further, the present invention also relates to a silicon carbide sintered body which propagates ultrasonic waves, and particularly to a silicon carbide sintered body of high density and high purity, which can be applied to components for semiconductor production apparatuses, components for electronic information equipment, and various structural components for vacuum devices and the like, and which can suitably be used as an ultrasonic resonance plate or an ultrasonic diaphragm.
2. Description of the Related Art
Conventionally, ultrasonic cleaning which allows cleaning of materials to be cleaned by means of ultrasonic waves, has been carried out in various fields. In the above-described ultrasonic cleaning, a material to be cleaned is immersed in a cleaning liquid accommodated in a cleaning vessel. An ultrasonic oscillator disposed at the bottom of the cleaning vessel is oscillated at a predetermined frequency. As a result, ultrasonic vibration is induced in the cleaning liquid, and impurities such as oil or dust, which adhere to the surface of the material to be cleaned, and to the vicinity thereof, are removed due to cavitation of the cleaning liquid.
As the cleaning vessel used for the above-described ultrasonic cleaning, conventionally, for example, a cleaning vessel 10 as shown in FIG. 3 has been known. The cleaning vessel 10 includes an outer cleaning vessel 12 made of metal, resin, or the like, and an inner cleaning vessel 11 disposed to be accommodated in an interior of the outer cleaning vessel 12. An ultrasonic propagation medium 13 is accommodated in a clearance formed between the outer cleaning vessel 12 and the inner cleaning vessel 11, and an ultrasonic oscillator 5 is disposed at the bottom of the outer cleaning vessel 12. It is advantageous to use, as the cleaning liquid, a liquid such as acid, having a strong corrosiveness, from the standpoint of improving cleaning efficiency of the material to be cleaned. Therefore, conventionally, the inner cleaning vessel 11 has been generally made of quartz in a case of acid cleaning.
However, the inner cleaning vessel 11 made of quartz or the like has a problem in that it is apt to be deteriorated and broken by ultrasonic waves and durability thereof deteriorates, and particularly, such defects are remarkably caused in a peripheral edge portion at the bottom of the vessel. Further, there exists a problem in that propagation of ultrasonic waves is interfered and cleaning efficiency thereby deteriorates. Moreover, there also exists a problem in that sufficient corrosion-resistance to hydracid fluoride is not obtained and the vessel cannot be used when hydrofluoric acid or mixture of hydrofluoric acid and nitric acid, which is used very often for cleaning of semiconductor materials, is used as the cleaning liquid.
Furthermore, in the fields of semiconductors and ultrasonic vibration, quartz components which have been conventionally used, deteriorate or degenerate due to cleaning using chemicals such as hydrofluoric acid. Therefore, there has recently been remarked a high density silicon carbide sintered body having excellent resistance to heat, in which the above-described problems are not caused. Particularly, in the field of ultrasonic vibration, it is necessary that a silicon carbide sintered body propagates ultrasonic waves. Desirably, a sound velocity of propagated ultrasonic waves may be increased.
An object of the present invention is to solve the above-described conventional problems and achieve the following object. That is, an object of the present invention is to provide a long-lived cleaning vessel used for ultrasonic cleaning, which is easily manufactured and is also easy to handle due to a simple structure thereof and which has excellent durability, mechanical strength, and resistance to corrosion.
As a result of their diligent studies for solving the above-described problems, the present inventors noted that ultrasonic waves contacting a material to be cleaned, which is accommodated within a cleaning vessel, are apt to be reflected and propagated through a peripheral edge at the bottom of the cleaning vessel, the peripheral edge at the bottom of the cleaning vessel is apt to be broken due to the ultrasonic waves, and a portion in which the ultrasonic waves are introduced, is also apt to be broken due to the ultrasonic waves.
The present invention has been devised based on the above-described extended researches of the present inventors, and the above-described problem is solved by the following means.
In accordance with a first aspect of the present invention, there is provided a cleaning vessel for cleaning a material to be cleaned, by introducing therein ultrasonic waves, the cleaning vessel comprising a cleaning vessel main body in which the material to be cleaned is accommodated together with a cleaning liquid, and a layer of silicon carbide sintered body which propagates ultrasonic waves, wherein the layer of silicon carbide sintered body is formed at an inner side of the cleaning vessel main body at least on a bottom peripheral edge portion of the cleaning vessel main body and on a portion in which the ultrasonic waves are introduced.
In accordance with a second aspect of the present invention, the layer of silicon carbide sintered body is comprised of a silicon carbide sintered body of which density is 2.9 g/cm3 or greater.
In accordance with a third aspect of the present invention, the layer of silicon carbide sintered body is comprised of a silicon carbide sintered body in which the total content of elements other than Si, C, O, N, halogen, and rare gas is 10 ppm or less.
In accordance with a fourth aspect of the present invention, the layer of silicon carbide sintered body is comprised of a silicon carbide sintered body of which volume resistivity is 1 xcexa9xc2x7cm or less.
In accordance with a fifth aspect of the present invention, the layer of silicon carbide sintered body is comprised of a silicon carbide sintered body which can be heated by turning on electricity.
In accordance with a sixth aspect of the present invention, the layer of silicon carbide sintered body formed on the bottom peripheral edge portion at the inner side of the cleaning vessel main body, has a passage for a cooling medium.
In accordance with a seventh aspect of the present invention, providing that a wavelength of introduced ultrasonic waves is xcex, an acoustic velocity of the ultrasonic waves is "ugr", and a frequency of the ultrasonic waves is f, thickness (b) of the layer of silicon carbide sintered body when oscillated a wavelength l/m, is represented by the following expression:
b=(xcex/m)n=("ugr"/mf)n 
(n represents an integer).
In accordance with an eighth aspect of the present invention, the layer of silicon carbide sintered body is formed on an entire surface at an inner side of the cleaning vessel main body.
In accordance with a ninth aspect of the present invention, the cleaning vessel main body has a heat resisting temperature of 120xc2x0 C. or higher.
In accordance with a tenth aspect of the present invention, the cleaning vessel main body has high chemical resistance.
In accordance with an eleventh aspect of the present invention, the cleaning vessel main body is made of thermosetting resin.
In accordance with a twelfth aspect of the present invention, the thermosetting resin is any one of polyvinyl chloride and polytetrafluoroethylene.
According to the first aspect, the cleaning vessel is comprised of the cleaning vessel main body in which the material to be cleaned is accommodated together with the cleaning liquid, and the layer of silicon carbide sintered body. When ultrasonic waves are oscillated from an outer side to an inner side of the cleaning vessel, the ultrasonic waves propagate through the cleaning vessel main body and are introduced into the cleaning vessel main body. At this time, the layer of silicon carbide sintered body is formed at the inner side of the cleaning vessel main body at least on the bottom peripheral edge portion and on a portion in which the ultrasonic waves are introduced. The layer of silicon carbide sintered body propagates ultrasonic waves, and therefore, the ultrasonic waves are propagated into the cleaning vessel irrespective of the presence of the layer of silicon carbide sintered body. For this reason, when the material to be cleaned is accommodated together with the cleaning liquid in the cleaning vessel main body, ultrasonic waves introduced into the inner side of the cleaning vessel main body, propagate the cleaning liquid (that is, ultrasonic vibration is induced in the cleaning liquid), and contact the material to be cleaned. At this time, impurities such as oil or dust, which adhere to the surface of the material to be cleaned, and to the vicinity thereof, are removed due to a vibration action (cavitation) of the cleaning liquid, and ultrasonic cleaning of the material to be cleaned is carried out.
In the ultrasonic cleaning, even if the ultrasonic waves contacting the material to be cleaned, concentrate on the bottom peripheral edge portion of the cleaning vessel main body, the layer of silicon carbide sintered body having high hardness, durability, and strength is formed on the bottom peripheral edge portion, thereby causing no breakage or the like on the bottom peripheral edge portion. Further, the layer of silicon carbide sintered body having high hardness, durability, strength, and chemical resistance is formed on a portion of the cleaning vessel main body in which the ultrasonic waves are introduced. Therefore, no breakage or the like is caused in the portion influenced by a great shock of ultrasonic waves.
In the above-described cleaning vessel, the layer of silicon carbide sintered body is merely formed at the inner side of the cleaning vessel main body. Therefore, the cleaning vessel is easily manufactured and is easy to handle due to a simple structure thereof.
According to the second aspect, in the cleaning vessel, the layer of silicon carbide sintered body is comprised of a silicon carbide sintered body of which density is 2.9 g/cm3 or more. The layer of silicon carbide sintered body has excellent durability and mechanical strength. Accordingly, in the above-described cleaning vessel, deterioration, breakage, or the like thereof caused by ultrasonic waves are effectively prevented.
According to the third aspect, in the cleaning vessel, the layer of silicon carbide sintered body is comprised of a silicon carbide sintered body in which the total content of elements other than Si, C, O, N, halogen, and rare gas is 10 ppm or less. Accordingly, when ultrasonic cleaning is carried out using the cleaning vessel, there is a reduced risk of the material to be cleaned being contaminated by these elements, that is, impurities, which are dissolved into the cleaning liquid to contaminate the cleaning liquid.
According to the fourth aspect, in the cleaning vessel, the layer of silicon carbide sintered body is comprised of a silicon carbide sintered body of which volume resistivity is 1 xcexa9xc2x7cm or less. Accordingly, the layer of silicon carbide sintered body is easily subjected to processing such as electric discharge machining. Further, static electricity is eliminated, and charging is not easy to occur in the silicon carbide sintered body. As a result, in this cleaning vessel, adhesion of particles caused by charging is effectively prevented.
According to the fifth aspect, in the cleaning vessel, the layer of silicon carbide sintered body is comprised of a silicon carbide sintered body which can be heated by turning on electricity. Accordingly, the cleaning vessel is heated when the layer of silicon carbide sintered body is charged with electricity. The above-described cleaning vessel heated to a fixed temperature is easy to introduce the ultrasonic waves therein, and is thereby excellent in the ultrasonic cleaning efficiency.
According to the sixth aspect, in the cleaning vessel, the layer of silicon carbide sintered body formed on the bottom peripheral edge portion at the inner side of the cleaning vessel main body, has a passage for a cooling medium. For this reason, when the silicon carbide sintered body or the cleaning vessel is in an overheat state, the silicon carbide sintered body or the cleaning vessel is cooled only by flowing a cooling medium through the passage for a cooling medium. As a result, overheat of the cleaning liquid accommodated in the cleaning vessel main body is effectively restrained.
According to the seventh aspect, in the cleaning vessel, providing that a wavelength of introduced ultrasonic waves is xcex, an acoustic velocity of the ultrasonic waves is "ugr", and a frequency of the ultrasonic waves is f, thickness b of the layer of silicon carbide sintered body when oscillated a wavelength l/m, is represented by the following expression:
b=(xcex/m)n=("ugr"/mf)n 
(n represents an integer).
The layer of silicon carbide sintered body in the cleaning vessel resonates with the introduced ultrasonic waves a half-wave length, and the ultrasonic waves are transmitted therethrough without being reflected. For this reason, ultrasonic waves introduced into the cleaning vessel, contact the material to be cleaned, without being interfered. As a result, the cleaning vessel is extremely excellent in the ultrasonic cleaning efficiency.
According to the eighth aspect, in the cleaning vessel, the layer of silicon carbide sintered body is formed on the entire surface of the inner side of the cleaning vessel main body. Therefore, the cleaning vessel has excellent durability to the ultrasonic waves, and also has excellent mechanical strength. In the above-described cleaning vessel, the cleaning vessel main body does not directly contact the cleaning liquid accommodated therein, and the silicon carbide sintered body directly contacts the cleaning liquid. The layer of silicon carbide sintered body has excellent corrosion resistance. Therefore, even if the cleaning liquid is a liquid such as acid, having a strong corrosiveness, no deterioration is caused in the layer of silicon carbide sintered body. As a result, the cleaning vessel has excellent corrosion resistance and can be used for a long life period.
According to the ninth aspect, in the cleaning vessel, the cleaning vessel main body has a heat resisting temperature of 120xc2x0 C. or more. Accordingly, in this cleaning vessel, ultrasonic cleaning at a high temperature can be carried out.
According to the tenth aspect, in the cleaning vessel, the cleaning vessel main body has a high chemical resistance. In this cleaning vessel, even when the cleaning vessel main body accommodates therein a cleaning liquid such as acid having a strong corrosiveness, it has excellent corrosion resistance. As a result, the cleaning vessel has excellent durability and can be used for a long life period.
According to the eleventh aspect, in the cleaning vessel, the cleaning vessel main body is made of thermosetting resin. For this reason, there is no possibility that the cleaning vessel main body be deformed or the like due to heating at the time of ultrasonic cleaning. As a result, the cleaning vessel is easy to manufacture, and is excellent in durability, mechanical strength, and the like.
According to the twelfth aspect, in the cleaning vessel, the thermosetting resin is any one of polyvinyl chloride and polytetrafluoroethylene. For this reason, the cleaning vessel is easy to manufacture and is excellent in durability, mechanical strength, and corrosion resistance.
Another object of the present invention is to provide a silicon carbide sintered body of high density and high purity, which can be applied to components for semiconductor production apparatuses, components for electronic information equipment, and various structural components for vacuum devices and the like, and which can suitably be used as an ultrasonic resonance plate or an ultrasonic diaphragm, and when used as the ultrasonic resonance plate or ultrasonic diaphragm, which can be easily processed, and further which can be made thinner while maintaining sufficient mechanical strength.
The above-described object can be solved by the following means. That is, in accordance with a thirteenth aspect of the present invention, there is provided a silicon carbide sintered body which can propagate ultrasonic waves, wherein an acoustic velocity of ultrasonic waves propagated therethrough is 4000 to 20000 m/s.
In accordance with a fourteenth aspect of the present invention, there is provided a silicon carbide sintered body in which the acoustic velocity of ultrasonic waves propagated therethrough is 4000 to 11000 m/s, and the silicon carbide sintered body is used as an ultrasonic resonance plate.
In accordance with a fifteenth aspect of the present invention, there is provided a silicon carbide sintered body in which the acoustic velocity of ultrasonic waves propagated therethrough is higher than 11000 m/s and is 20000 m/s or less, and the silicon carbide sintered body is used as an ultrasonic diaphragm.
In accordance with a sixteenth aspect of the present invention, there is provided a silicon carbide sintered body in which the density of the silicon carbide sintered body is 2.9 g/cm3 or greater.
In accordance with a seventeenth aspect of the present invention, there is provided a silicon carbide sintered body in which the total content of elements other than Si, C, O, N, halogen, and rare gas is 10 ppm or less.
In accordance with an eighteenth aspect of the present invention, there is provided a silicon carbide sintered body in which the volume resistivity of the silicon carbide sintered body is 1 xcexa9xc2x7cm or less.
In accordance with a nineteenth aspect of the present invention, there is provided a silicon carbide sintered body which is obtained by carrying out hot press for a mixture of silicon carbide powder and nonmetal based sintering additive at the temperature of 2000 to 2400xc2x0 C. and at the pressure of 300 to 700 kgf/cm2 in a non-oxidizing atmosphere.
In accordance with a twentieth aspect of the present invention, there is provided a silicon carbide sintered body which is obtained in such a manner that a mixture of silicon carbide powder and nonmetal based sintering additive is heated in a mold at the temperature of 80 to 300xc2x0 C. for 5 to 60 minutes to form a molded body, and thereafter, the molded body is subjected to hot press at the temperature of 2000 to 2400xc2x0 C. and at the pressure of 300 to 700 kgf/cm2 in a non-oxidizing atmosphere.